The present invention relates to packaged food articles and to methods of their preparation. More particularly, the present invention relates to packaged cultured dairy product articles to their methods of preparation.
The present invention provides further improvements in packaged food articles such as refrigerated cultured dairy product articles. A variety of cultured dairy products are packaged in relatively small, plastic containers. For example, refrigerated yogurt products can be packaged in single serving plastic containers. In certain products, the plastic containers generally include a plastic cup having an upper opening through which the yogurt is filled. After filling, the opening is scaled with an overlaying flexible membrane that seals the opening after filling. The plastic cups are designed to be stackable upon each other with the bottom of one cup resting upon the sealing membrane of a lower cup.
Certain foods continue to release gases into the headspace after filling. For example, certain vat cultured yogurt products evolve CO2 gas after filling into the headspace. If the plastic container is fabricated having too low of a CO2 flux through the container (i.e., lower than the rate of release from the food), then CO2 can build up in the headspace. Even minor amounts of CO2 build up in the headspace can cause the flexible seal membrane to undesirable bow upwards forming a bowed membrane having a convex shape. Such containers may be desirable for other reasons, e.g., due to lower cost of materials, even though possessing low particular gas flux properties.
A bowed or convex membrane is undesirable for at least two reasons. First, a bowed membrane aggravates stacking problems of containers upon each other. To conserve display space, at retail, yogurt containers are typically stacked at least two items high upon each other. Such stacking is usually done manually. Having an outwardly bowed membrane makes such manual stacking more difficult or even impossible. Also, even if stacked, such stacking arrangements are less stable and more prone towards collapse especially as the consumer selects a container from a stacked array. A second reason resides in consumers"" perceptions and apprehensions regarding a bowed membrane. Consumers can erroneously believe that the bulging or bowing is caused by contamination or by some other product defect. Since yogurt products sell in highly competitive markets, even minor perceived imperfections can result in loss of sales.
One solution to minimize bowing is to package the food products under vacuum. By having a vacuum in the headspace, room is provided for the released gas. However, vacuum packaging is expensive, has slow packaging line speeds, and may not be practical for food products that are subject to damage when exposed to vacuum.
The present invention provides improvements in packaged foods that minimize the problems of bowing caused by such gas release without need for vacuum packaging. One advantage is that costs associated with such vacuum packaging can be avoided. A further advantage is that foods sensitive to vacuum can be packaged. Still another advantage is that foods containing live cultures such as cultured dairy products can be provided that comprise containers fabricated from low cost low CO2 permeability materials. Still another advantage resides in minimization of the stacking problems associated with packages suffering from bowing.
Still another advantage of the present invention is that rather than merely preventing a bowed flexible membrane or even providing merely a flat flexible membrane, the present invention can provide a xe2x80x9cdishedxe2x80x9d flexible membrane or inwardly curved. A dished membrane is one that is concave in shape. Such a shape desirably conveys to consumers an impression of having been vacuum sealed even though not so prepared. Moreover, the concave shape desirably suggests to consumers that seal integrity has been maintained.
Surprisingly, the present invention resides in the counter intuitive initial addition to the headspace prior to sealing of the very gas that is released by the contained food stuff. By adding higher concentrations of CO2 initially to the headspace, flux or loss of CO2 from the headspace through the container is initially accelerated by its higher concentration. Since air permeability into the container is slower than CO2 loss, a partial vacuum is formed in the sealed headspace at least during the short time from production to sale. The partial vacuum provides volume for the evolved CO2 without causing bowing. Indeed, enough vacuum is created to not only allow for the evolved gas but also to provide the desirable dishing membrane feature.